Optical communications modules used in optical networks for transmitting and receiving optical data signals come in a variety of configurations. An optical communications module may be an optical receiver module with receive-only capabilities, an optical transmitter module with transmit-only capabilities or an optical transceiver module with transmit and receive capabilities. A typical optical transmitter or transceiver module has a TOSA that includes at least one laser diode and various other electrical components. A laser driver circuit of the module that can be either external to or internal to the TOSA outputs an electrical drive signal to each respective laser diode to cause the respective laser diode to be modulated. When the laser diode is modulated, it outputs optical signals that have power levels corresponding to logic 1s and logic 0s. An optics system of the module focuses the optical signals produced by each respective laser diode into the end of a respective transmit optical fiber held within an optical connector module that connects to the optical transmitter or transceiver module.
A typical optical receiver or transceiver module has a ROSA that includes a receiver IC, at least one receive photodiode and various other electrical components. An optics system of the ROSA focuses an optical data signal that is output from the end of an optical fiber onto a photodiode of the ROSA. The photodiode converts the incoming optical data signal into an electrical analog signal. An electrical detection circuit, such as a transimpedance amplifier (TIA), receives the electrical signal produced by the photodiode and outputs a corresponding amplified electrical signal, which is processed by other circuitry of the ROSA to recover the data.
One well known type of optical communications module is a transistor outline (TO)-can assembly. A typical TO-can assembly includes a header and a cap. The header and the cap are typically made of a metal material, such as stainless steel, for example, to allow them to be welded together. The TO-can assembly is generally cylindrical in shape. The header has an upper mounting surface on which a laser diode and/or a photodetector and other electric components are mounted. Electrical circuitry of the TOSA or ROSA is electrically interconnected with proximal ends of electrical leads that pass through the header and have distal ends that are disposed on the opposite side of the header for electrically interconnecting the TOSA or ROSA to external electrical circuitry, such as electrical circuitry of a printed circuit board (PCB).
TO-can assemblies are typically not used in WDM applications that use more than two wavelengths for a number of reasons. One reason is that TO-can packages are relatively bulky in size and shape and, therefore, are not well suited for incorporating multiple sets of discrete optics and other components that are needed for transmitting or receiving optical data signals of multiple wavelengths. Planar lightwave circuits (PLCs), also known as photonic integrated circuits (PICs), are better suited for WDM applications because they allow many optical, optoelectronic and electrical components to be integrated on the same substrate and packaged in a relatively small package. PLCs, however, require special equipment to manufacture them, which leads to large capital investment for plant retooling and time delays in bringing the products to market.
Although it is known to package bi-directional optical subassemblies (BOSAs) in TO-can packages, the existing BOSAs are only capable of using two wavelengths and therefore have only two TO-can devices. It is also known to make three-channel, or tri-, OSAs that have three TO-can devices. The BOSA and tri-OSA packages are also relatively large in size. In addition, due to the configuration of the focusing optics they employ, the known BOSAs and tri-OSAs are limited to having a wavelength spacing between the TO-can devices that is greater than 10 nanometers (nm), which limits the wavelengths that can be used by the BOSAs and tri-OSAs. The focusing optics system configuration also limits the number of channels and wavelengths to three at most due to limitations on the ability of the focusing optics to achieve a great enough focal length if more than three TO-can devices are included. Due to all of these limitations, the existing BOSAs and tri-OSAs are not practical for use in applications that require smaller packaging; or that require more than two or three wavelengths.
Cloud computing and Fourth Generation Long Term Evolution (4G LTE) networks are driving very large demands for increased bandwidth. A need exists for WDM TOSA and ROSA assemblies that are capable of transmitting and receiving optical data signals, respectively, having more than three wavelengths. A need also exists for WDM TOSA and ROSA assemblies that can be packaged in smaller packages than those used for currently available BOSAs and tri-OSAs. A need also exists for WDM TOSA and ROSA assemblies that can be manufactured without requiring a large amount of plant retooling or capital investment and that can be made available in the market relatively quickly.